Preventing evaporation from oil storage tanks



Jan. 5, 1943. D, w, AYNE 2,307,508

PREVENTING EVAPORATION FROM OIL STORAGE TANKS Filed Oct. 4, 1939 2 Sheets-Sheet 1 David @fdfliZG lNVENTOR M ATTORNEY'Y v I Jan. 5, 1943 D. w. JAYNE 2,307,508

PREVENTING EVAPORATION FROM OIL STORAGE TANKS Filed Oct. 4, 1939 2 Sheets-Sheet 2 flan m WJayzw INVENTOR Q ATTORNEY,

I this loss.

evaporation losses involves placing a pontoon roof 7 within the tank. A pontoon root is a self-contained element fitting within the shell of a storage Patented Jan. 5, 1943 PREVENTTNG avaroaarron FROM on. sronaoa TANKS David w. Jayne, Wilmington; DeL, assignortto E. I. du Pont de Nemours & Company, Wilmington, DeL, a' corporation of Delaware Application October 4, 1939, Serial No. 297,797

1 Claim. (01. 220-26) This invention relates to tanks in which volatile liquids are stored and more particularly to active storage tanks containing gasoline or other volummoithe gasoline in the tanks changes constantlyiby reason of additions and withdrawals, the amount of the vapors lost becomes enormous.

' r Vapors of volatile liquids are also lost even when the content of the tank is not changed because of ithe expansion and contraction of the, vapors above the liquid surface due to changes in temsrperature.

devices have been proposed to eliminate One method now in use to eliminate tank and replacing the'usual roof of a storage tank. Such a pontoon is adaptable to construction in new storage tanks but is not-economical for existing tanks as the original root of the tank ume of the pontoon element.

- Another disadvantage of the pontoon roof is i that rain must be collected in a basin and allowed to overflow through a syphon drain into the liquid content below and settle to the bottom of the tank and must be removed from time to time. It is, therefore, an object of this invention to provide means for preventing the evaporation-oi the volatile components of liquids which may be applied to either existing or new tanks. Another object of this invention is the provision of a device adapted to float On'the surface of the liquid in a storage tank through which vapors cannot pass and is highly resistant to liquids which are likely to be stored in such tanks. A still further object is the provision of a floating device which may be installed in a storage tank by introducing the materials through the conventional manhole with which practically all such tanks are provided. Other objects will appear as the description of the invention proceeds.

These objects are accomplished by providing a layer of buoyant material which is covered by a membrane of fabric coated with a material which 65 that when the tank is emptied completely and I sented as I.

is not penetratedby the vapor of the liquid contained in the tank and which will float on the surface of the liquid and is non-rigid.

The invention will be more clearly understood by reference to the drawings in which Figure 1 is a top plan view-along the line l-,| of Figure 3. In this figure parts are broken away to show the construction and arrangement of the parts.

Figure 2 is a detailed view of a vertical section along lines 2-2 of Figure l. I

Figure 3 is a diagrammatic section of a tank in which the product of the invention is installed.

Figure 4 is a plan view similar to Figure 3'except that the means for preventing the escape of vapors about the central support is difierentas will be explained hereinafter. In all the figures the same numerals refer to the same parts. i

In Figure 1 the wall of the tank is indicated as I. The buoyant material 'is shown as 2 and the membrane stretched over and secured to the buoyant material is represented as 3. In Figure 2 the detail ofthe method 01' preventing evaporation losses at the periphery of the buoyant material is shown. In this figure the membrane 3 extends over the end oi. the buoyantmaterial 2 and forms a wiper which bears against the tank 1. An auxiliarywiper 4 is'provided'to further prevent losses. In Figure 2 this is illustrated as being inserted between two blocks 5 and '6 "of buoyant material. The auxiliary wiper 4' may be ,attached to the bottom of the buoyant material 2 or a complete second membrane may be provided over the entire lower side of the buoyant material.

In Figure 3 the walls of the tank are repre- The buoyant material and membrane are shown as 2 and 3, respectively. The root is indicated as I, while 8 is a vent to allow air to enter and escape from the tank as it is being emptied and filled. The central support The description of Figure 41s the same as that of Figure 3 except that the means for preventing losses about the central or other support is different. In this figure a tubular pieceot membrane I2 is attached to a collar l3 and also to the :buoyant material 2. The length of this tube is such the buoyant material 2 is close to the bottom of the tank, the tube will be just extended entirely in a vertical position.

In the operation of the device, 011 or other volatile liquid is pumped in through the conduit or pipe it]. As the surface of the liquid rises the buoyant material floats on its surface and thereby prevents the evaporation of the liquid over the surface of the liquid where it is present. At the,

edges of the buoyant material the wipers 4 prevent the evaporation through the small passages bee tween buoyant material and the walls or supports I of the tank. As the liquid in the tank rises, the

wipers take the position shown in the heavy lines in Figures 3 and 4. In Figure 4 the tubular mem- H ber i2 will fold back upon itself as shown in'solid lines in this figure. through conduit in from the tank, the wipers take As the liquid is emptied closed within the tank is to introduce cork blocks through the manhole II and place them close to each other over the entire area of the floor of the tank. The membrane is then placed over the cork blocks and fastened by any suitable means such as by staples to the. blocks. It is advisable to seal the heads of the-staples with a suitable cement.

It is to be understood that the figures are diagrammatic and not drawn to scale and that any of the parts may be enlarged or diminished without departing from the spirit of the invention. ,For example the blocks of buoyant material may be much larger. than those shown in Figure l I or for certain purposes they may be relatively small. In any event they should not be placed so close together or fastened so as to be rigid since the position shown in the dotted lines in Figures 3 and 4, and the tubular member of Figure .4 will approach its fully extended position as the buoyant material reaches the bottomof the tank.

WhileI have described the invention as suitable for gasoline, it is' to be understood that it is equally suitable for crude petroleunnnaphtha; benzene, and practically all volatile.organicliquids. It is likewise suitable for applicationto tanks wherein non-volatile liquids having volatile components are stored. It is also to-be=understood that any buoyant material sumciently light tofloat upon a liquid and support an impermeable membrane is suitable in the invention. I prefer, however, to use cork orbalsa wood blocks. These blocks may be impregnatedor coated with resins, lacquers, or Y any material which is efiective in preventing the absorption of the liquid with which it is in contact.

The membranemay be any suitable impregnated fabric. I have found however, that-a strong woven canvas impregnatedwith neoprene which is a rub ber like plastic polymer of 2 chloro 1,3, butadiene ,on one or both sides is particularly well adaptedto'the present ,invention due to its imperviousness to petroleum and similar liquids. This membrane maybe prefabricated to the'desired dimensions or introduced into thetank. in segments and assembled withinithe tank. -Any seams made withinthe tank and not previously rendered imperviousmay be made so-by an appropriate cement such as neoprene cement.

One method oi installing the device, herein-dismany advantages flow from an arrangement wherein the blocks are placed in an articulated position; that is, whe'rethere is a slight space between the blocks, and they may move slight- 131 with relation to each'other. -When'so arranged the entire covering of the liquid rises and falls smoothly'and evenly and does-not bind when passing'over rivets or other protuberances in the walls of the tanker other supports. s

It is apparent that many'widely different embodiments of this invention may be made without departing fromthe spirit and scope thereof. and therefore. it'is' not intended to'be limited except as indicated in the appended claim.

I Claim: I I I A floating roof for installation in'a storagetank operating therewith and withthe tankwall.

' DAVID w. am.

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